The best way to read OO code?

This might be a silly question.

What's the best way to read a complicated, interweaved OO code?:

1. Start from the main() and go through each function call to get to know the classes?
2. Start from the beginning of the 1st cpp file and read every file back-to-back?
3. Another way?

Thanks. Good day to all.

Read the header files, as with any code. For OO code, I would read the base classes first and then the implementations (going down the tree).

I like to start from main (or a class) and trace backward from there. That usually works pretty good since most OOP uses the 'top-down' design approach. That way, you get to study the abstraction before you get to the 'guts' of the code.